DUSTIXG COTTON FROM AIHPlAtfES. 27 
at a rate of about 30 revolutions of the crank per minute. A few 
special studies were made to determine the effect of variation- in 
the speed of cranking. Beyond a certain point the rate of dust de- 
livery was not increased in proportion to an increase in the rate of 
paddle revolution, owing to the fact that after being speeded up 
beyond this point the paddle revolved so fast that the spaces between 
the blades did not have time to pick up a full load of dust, and when 
the paddle was operated at a very high speed the dust delivery was 
somewhat reduced by the fact that the blades tended to cut out a 
channel and the dust did not have time to drop between them. 
As finally settled upon for use in the field applications, a full 
opening of the feeder valve with a hand crank operated at about 30 
revolutions per minute emptied the hopper in approximately 2 miles, 
depending on the speed at which the plane was flown. In other words, 
it was necessary to take at each trip a strip of about 60 feet of cotton 
if the poundage of dust utilized per acre was not to exceed that dis- 
tributed by the ground machines. Any additional width which could 
be taken of course constituted a reduction in the poundage per acre 
delivered. 
These figures were obtained by straightaway flights with the 
feeder operating continuously from the start until the hopper was 
empty. When this hand-crank hopper was placed in service in 
actually dusting cotton fields, a serious difficulty developed, due to 
variations in the rate of flying speed of the plane as it crossed back 
and forth over the fields. In turning to enter a field the plane would 
be flying probably 100 feet or more in the air. It would be man- 
euvered into position and then would glide downward with a throt- 
tled motor into the edge of the field. It was often still descending 
for perhaps the first 100 feet after crossing the edge of the cotton, 
especially if any obstructions intervened along that margin of the 
field. The feeder would be opened and the crank started almost as 
soon as the plane passed the edge of the cotton. The dust would be 
blown out behind the plane for some distance, but often for about 
150 feet after the plane entered the field it was still gliding down- 
ward, and thus traveling at a reduced ground speed. The result 
was that the dust being put out at the normal rate spread over a 
rather wide strip at the edge of the field. Then the motor was grad- 
ually speeded up as the pilot neared the elevation he desired, and 
when he reached this point he "gave her the gun" to maintain a 
safe flying speed at the low level across the field. This rapid in- 
crease in speed, with no change in the rate at which the dust was 
delivered, resulted in a very wide strip being treated at the edge of 
the field, the margins being pulled in rapidly to a much narrower 
strip across the center of the field, where the plane was traveling at 
full speed. Then, when the plane reached the far edge of the field, 
it zoomed upward quickly and blew back into the field the dust 
which was delivered as the feeder was being cut off. This practi- 
cally reversed the conditions experienced while entering the field. 
The zooming not only decreased the ground speed of the plane but 
blew the dust downward and backward from a distance beyond the 
field. 
An outline of the dust cloud produced by this trip across t\\v field 
presented somewhat the shape of an hour glass, wide at both ends 
and narrowing rapidly to the middle. To avoid leaving untreated 
